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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1003-1006 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model Hamiltonian, designed to allow larger systems to be treated with the Green's function Monte Carlo method, is introduced for atomic and molecular systems. The model reduces the statistical variance associated with Green's function Monte Carlo calculations by reducing potential energy fluctuations in the core regions. By performing calculations of Li, LiH, and Li2 we show that this method can be used to obtain energy differences with much less computer time than required for the complete interaction. Increases in efficiency for larger systems will be even greater.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2868-2874 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An implementation of the domain Green's function Monte Carlo algorithm is described. Unlike the short time approximation, the method is variational and exact within the limits of the fixed node approximation. The systems investigated include LiH, Be in the ground and first excited states, a study of the C2v insertion pathway of Be into H2, and H2O. We predict a barrier of 0.190 hartree for the insertion reaction with a statistical accuracy of ±2%. Better than 90% of the correlation energy is recovered in each case, which makes these some of the most accurate computations to date.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1906-1906 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 10294-10299 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ground-state energies of the two isomers of the methanol-water dimer, with water-donor (WM) and methanol-donor (MW) structures, have been calculated using the diffusion Monte Carlo (DMC) method with constraint dynamics. Unlike the rigid-body DMC, this method permits the internal rotations of the hydroxyl and methyl groups of methanol about the C–O bond. The DMC calculations were performed for the isotopomers CH3OH(centered ellipsis)H2O, CH3OD(centered ellipsis)H2O, and CD3OH(centered ellipsis)H2O. The calculations with the internal rotation of the methyl and hydroxyl groups of methanol included resulted in a much larger ground-state energy gap between the WM and MW isomers than those in which these internal rotations were frozen. This result demonstrated the critical importance of including the internal hydroxyl and methyl rotations in the DMC calculations aimed at predicting accurately the relative stabilities of the two isomers of the methanol-water dimer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10181-10184 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: HF vibrational frequency shifts for ArnHF (n=1–14) clusters have been determined for the first time using quantum 5D bound state calculations. Our results for n=1–4 clusters are in very good agreement with the available experimental data. The size dependence of the redshift is predicted to be very nonmonotonic. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 7166-7181 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper presents a theoretical study of the size evolution of equilibrium structures and approximate HF vibrational red shifts for ArnHF van der Waals clusters, with n=1–14. Pairwise additive ArnHF intermolecular potential energy surfaces were constructed from spectroscopically accurate Ar–Ar and anisotropic Ar–HF potentials. The latter depend on vibrational excitation of the HF monomer. The global and energetically close-lying local minima of ArnHF, n=1–14, for HF v=0 and v=1, were determined using simulated annealing followed by a direct minimization scheme. For ArnHF clusters with n≤8, the lowest-energy structure always has HF bound to the surface of the Arn subunit. In contrast, for n≥9, the global minimum of ArnHF corresponds to HF inside a cage. Ar12HF has the minimum-energy configuration of an HF-centered icosahedron, which appears to be unusually stable. Size dependence of the HF vibrational red shift in ArnHF (n=1–14) clusters was investigated by means of a simple approximation, where the red shift was represented by the energy difference between the global minima of a cluster obtained for HF v=0 and v=1, respectively. The approximation reproduced rather accurately the experimentally determined variation of the ArnHF red shift with the number of Ar atoms, for n=1–4, although it overestimated their magnitude. For larger ArnHF clusters, 4〈n≤14, a nonmonotonic, step-like dependence of the red shift on the cluster size is predicted, which can be interpreted in terms of changes in the minimum-energy cluster geometries. The predicted red shift for the icosahedral Ar12HF, where the first solvation shell is full, is 44.70 cm−1, which is only 5.4% higher than the experimental HF vibrational red shift in an Ar matrix, of 42.4 cm−1.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6359-6361 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum 5D bound state calculations for the fully solvated Ar12HF cluster, with the Ar atoms frozen at their icosahedral equilibrium geometry, gave the HF vibrational redshift of 42.46 cm−1. This value is equal to that measured for HF in an Ar matrix, 42.4 cm−1.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8310-8320 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Size evolution of the equilibrium structures of ArnH2O van der Waals clusters with n=1–14 has been investigated. Pairwise additive intermolecular potential energy surfaces (IPESs) for ArnH2O clusters were constructed from the spectroscopically accurate Ar–Ar and anisotropic 3D Ar–H2O potentials. For each cluster size considered, we determined the global minimum of the respective IPES and several other lowest-lying ArnH2O isomeric structures. This was accomplished by using simulated annealing followed by a direct minimization scheme. The minimum-energy structures of all ArnH2O clusters considered in this work are fully solvated; up to n=12, the Ar atoms fill a monolayer around H2O. For n=12, the optimal Ar12H2O structure has the Ar atoms arranged in a highly symmetrical icosahedron, with H2O in its center. The icosahedral Ar12H2O structure is exceptionally stable; the energy gap separating it from the next higher n=12 isomer (289.55 cm−1) exceeds that for any other cluster in this size range. The observed preference for solvated ArnH2O structures was carefully analyzed in terms of the relative energetic contributions from Ar–Ar and Ar–H2O interactions. For n≤9, the monolayer, cagelike geometries are favored primarily by providing optimal Ar–H2O interactions, significantly larger than for alternative ArnH2O structures. For n(approximately-greater-than)9, the solvated ArnH2O isomers offer the best Ar–Ar packing, in addition to the strongest total Ar–H2O interactions. A detailed comparison was made with the minimum-energy structures of ArnHF clusters, determined by us recently [J. Chem. Phys. 100, 7166 (1994)], revealing interesting differences in the growth patterns of the optimal cluster structures.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 1829-1841 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The HF vibrational frequency shifts for ArnHF van der Waals (vdW) clusters with n=4–14 are predicted to be strongly isomer-specific, providing distinct spectroscopic signatures for different cluster isomers. This represents an extension of our recent studies of the size dependence of the vibrational frequency shift for ArnHF clusters [J. Chem. Phys. 101, 6359, 10 181 (1994)]. The HF vibrational frequency shifts calculated for the two or three lowest-energy isomers of each cluster size considered differ by at least a couple of wave numbers. Their relative magnitudes directly reflect the number of Ar atoms that each ArnHF isomer has in the first solvation shell around HF. The calculations are performed on pairwise additive intermolecular potential energy surfaces constructed from spectroscopically accurate Ar–Ar and anisotropic Ar–HF potentials. In the frequency shift calculations, the Arn subunit is treated as rigid, frozen in the geometry of one of the global or local ArnHF minima found previously by simulated annealing [J. Chem. Phys. 100, 7166 (1994)]. The 5D coupled intermolecular vibrational levels of what is now effectively a floppy Arn–HF dimer, are calculated highly accurately by the quantum 5D bound state methodology which is described in detail. The 5D vdW vibrational zero-point energy of the ArnHF cluster affects significantly the energy gap between various isomers. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9228-9241 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A comprehensive study of the photodissociation of HF in ArnHF van der Waals clusters, with n=1−14,54, for an ultrashort δ(t)-pulse excitation, is presented. The emphasis is on the dependence of the photodissociation dynamics of the HF solute molecule on the size and geometry of the Arn solvent cluster. This cluster size range encompasses formation and closing of the first solvation shell, which occurs for n=12, the addition of the complete second solvent layer (n=54), as well as the change of the HF location in the cluster, from a surface site for n≤8 to the interior of a cage for n≥9 clusters. Evolution of the fragmentation dynamics is revealed by following how the H-atom kinetic energy and angular distributions, the survival probability, and cluster fragmentation patterns change as a function of the cluster size and structure. Classical trajectories are used to simulate the photodissociation dynamics. The probability distributions of the initial coordinates and momenta of the H and F atom are defined by accurate quantum five-dimensional eigenstates of the coupled, very anharmonic large amplitude intermolecular vibrations of HF in the cluster. All aspects of the dissociation process studied here are found to exhibit a strong dependence on the size and geometry of the ArnHF clusters. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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